The present invention relates to a method for producing a SOI substrate, and more particularly to a method for producing a SOI substrate wherein a semiconductor crystal layer is formed on an insulating film formed on a semiconductor substrate by epitaxial growth with using a semiconductor crystal of the substrate as a seed.
In this specification, the word SOI means a semiconductor crystal layer on an insulating film and widely represents semiconductors, which of course are not limited to silicon semiconductors.
SOI substrates has been produced conventionally by SIMOX (Separation by Implanted Oxygen) method, where oxygen atom is implanted to a semiconductor crystal substrate and then an insulating film is formed in the substrate by heat treatment, or by epitaxial growth method, where an opening is formed at an insulating film formed on a semiconductor substrate and then a semiconductor crystal layer is formed by epitaxial growth on the insulating film with using the semiconductor crystal of the substrate exposed through the opening as a seed.
A cross section of a conventional SOI substrate formed by epitaxial growth is shown in FIG. 4. This SOI substrate is produced as follows. An insulating film 2 is formed on a semiconductor substrate 1. An opening 3 is formed at the insulating film 2 with a resist film. Semiconductor crystal epitaxially grows from the semiconductor crystal exposed through the opening 3. The opening 3 is filled with the semiconductor crystal layer 4. The layer 4 further epitaxially grows on the upper surface of the insulating film 2 to finally form a SOI substrate wherein a semiconductor crystal layer is formed on an insulating film.
However, the conventional SIMOX method for producing a SOI substrate has a problem of semiconductor crystal damage (crystal defect) due to oxygen atom implantation. Further, in the conventional epitaxial growth method where an opening is formed at an insulating film on a semiconductor substrate and through the opening epitaxial growth is performed to form a semiconductor crystal layer, a satisfactory SOI substrate can not be obtained, because the semiconductor substrate is utilized as a seed for epitaxial growth whereby the crystal layer and the substrate connect with each other through the opening of the insulating film. In order to obtain a complete SOI substrate, a region including the opening must be removed, so that the SOI substrate undesirably becomes small.
In view of the above-mentioned problems, an object of the present invention is to provide a method for producing a substrate having a SOI structure wherein a semiconductor crystal layer by epitaxial growth on an insulating film and a semiconductor substrate under the insulating film are completely insulated from each other.
Another object of the present invention is to provide a substrate having a large SOI structure without any openings and to facilitate insulation between semiconductor layers in a three-dimensional IC by arranging the SOI substrates in a lamination.
Further object of the present invention is to provide a producing method by which a SOI substrate is easily made even from a semiconductor material which is hard to form monocrystal substrate.